ORTHOGONAL CONTACTS BETWEEN BENZENE RINGS - A SPECIAL TYPE OF SPECIFIC INTERMOLECULAR INTERACTIONS

The crystal structures of benzene and some of its derivatives are anal yzed in detail. The structures are characterized by orthogonal contact s between the benzene cycles (OBzC). Although the orthogonal contacts conflict with the close packing law, they are an important structure-f orming factor, being thus a specific type of intermolecular interactio ns. The OBzC system, which is inherent in the orthorhombic crystals of benzene, remains invariable in 2-aminophenol and 2-amino-4-chlorophen ol crystals, notwithstanding other specific interactions (H-banding an d halogen ... halogen contacts). OBzC are also observed in para- and o rtho-cresol crystals. A classification of OBzC is given, and an especi ally effective projection method (rectangular projection) is suggested .